# Ligand exchange reactions… are they one way or reversible?

Are ligand exchange reactions one-way reactions or reversible? I know this is a very silly question but its not said outright in any place...

For example, in my high school chemistry book, these two ligand exchange reactions are shown:

$$\ce{[Cu(H2O)6]^{2+} (aq) + 4Cl- (aq) <=> [CuCl_4]^{2-} (aq) + 6H2O (l)}$$

$$\ce{[Cu(H2O)6]^{2+} (aq) + 4NH3 (aq)-> [Cu(NH3)4(H2O)2]^{2+} (aq) + 4H2O (l)}$$

The first is reversible but the second is one-way

Also, my teacher stated that ligand exchange reactions are irreversible... this confused me further

Can someone please tell me what is right...

Let's take the binding of $\ce{O2}$ and $\ce{CO}$ to hemoglobin as example. $\ce{CO}$ does bind much better than $\ce{O2}$!
We can consider the reaction of oxygen-loaded hemoglobin with $\ce{CO}$ a ligand exchange reaction. If that would be completely irreversible, the logical consequences in the case of an intoxication would be: [...] six feet under ;)